Predicting culture positivity rates for Shiga toxin-producing Escherichia coli and Shigella species based on real time PCR cycle threshold values.

In 685 fecal specimens, culture positivity for STEC and Shigella/EIEC was highest when real-time PCR ct was ≤35, with 48.2% overall positivity and 22.0% at ct ≤35.

• Why it matters: Culture confirmation is resource-intensive, and ct values reflect bacterial load; the study sought a ct cutoff to focus culture on specimens most likely to yield positive results.
• What they did: The authors reviewed real-time PCR ct values from 685 fecal specimens, comparing culture outcomes across ct groups, including a subgroup with ct ≤35 (n=82).
• The result: Culture was three times more likely when ct was ≤35, but culture still occurred at ct >35; PCR-positive STEC from vulnerable patients or those with severe symptoms should be referred regardless of ct.

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